Musical instrument working through a keyboard and a photoelectric cell



Feb. 27, 1934. p. M, TQULQN 1,948,996

MUSICAL INSTRUMENT WORKING THROUGH A KEYBOARD AND A PHOTO-ELECTRIC CELLFiled May 14, 1928 4 Sheets-Sheet 1 Feb. 27, 1934. P. M. G. TOULONMUSICAL INSTRUMENT WORKING THROUGH A KEYBOARD AND A PHOTO-ELECTRIC CELLFiled May 14. 1928 Fig.8

4 Sheets-Sheet 2 7? 7716. you/o") Feb. 27, 1934. M Q TQULON 1,948,996

MUSICAL lNsTRUMENT WORKING THROUGH A KEYBOARD AND A PHOTO-ELECTRIC CELLFiled May 14.- 1928 4 Sheets-Sheet 3 Fig.12

Feb. 27, 1934. M, TO' LQN 1,948,996

MUSICAL INSTRUMENT WORKING THROUGH A KEYBOARD AND A PHOTO-ELECTRIC CELLFiled-May 14, 1928 4 Sheets-Shut 4 P 72 ow/an Patented Feb. 27, 1934 I:UNITED STATES PATENT OFFICE Pierre Marie Gabriel Toulornfuteaux,France, as-

signor to St de Recherches et de Perfectionnements industriels, Puteaux,,France, a company of fiance Application May'14, 1928, Serial No.277,667 In France May 19, 1927 7/ 6 Claims.

It has been proposed to reproduce sounds by means of devices consistingin a photoelectric cell placedin an electric circuit fed by a constantsupply, a light beam of constant intensity periodically interruptedimpinging .on said cell. This causes variations into the intensity ofthe currents flowing across the cell, which, after having beenconveniently amplified, are used for actuating a telephonic receiver ora loud speaker. It has been also proposed to insert between the lightsupply'and the cell a shutter or screen out out in convenient shape andhaving a relativ movement in reference with the light beam impinging onthe cell, so that during each luminous emission the quantity of lightimpinging on the cell is modulated according to the timbre of aninstrument, if said tone is to be reproduced. Musical instruments havebeen also described wherein to each note was corresponding a specialphotoelectric cell which, while said note was sounding, was lighted by asteady beam of constant intensity, a periodically modulating screencooperating with the cell; said screen being formed by a discconveniently cut out and rotating with such'a speed that the cutting outcrosses thelight beam with the frequency of the fundamental note, theshape of said cut out'giving to this note the required timbre.

These already known proceedings and devices show several drawbacks.Proceedings wherein the light is periodically interrupted at thefrequency of the required note do not allow the exact reproduction ofthe tone of an instrument. In none of the usual instruments occurs asudden and absolute stop of the vibratory movement during a determined,and even very short, part of the period of said movement. On thecontrary, it can always be represented by a continuous curve. Thiscannot be obtained by a broken illumination of the cell, and even if thequantity of light produced is modulated during the periods ofilluminations, this does:not amend said defect.

As for the above described proceeding using a The present invention hasfor its object to provide a device which will avoid said drawbacks, andto allow a continuous and exact reproduc tion of the tone of anyinstrument; and even new tones; the tone being known either by the curverepresenting its vibratory law, or by the range and relative intensitiesof the compounding harmonics; in this last'case a real synthesis of thesound is made. This can be accomplished by using a small number ofcells, say one for each octave.

The important feature of the invention is the following: luminous beamsare directed by any means, for instance, by mirrors actuated by thekeys, on the photoelectric cell and impinge on it after having crossed arotating slotted disc, the apertures of which succeed each other withthe frequency of the note which must be produced, and also one or moremodulating screens which give. to the sounded note the desired tone.

As explained above it is necessary to avoid sudden and periodical stopsin the illumination of the cell; an'dfor that purpose, the distancebetween the successive apertures 01 the disc and the dimensions of thewindows through which the beam passes before impinging on the cell areso determined that in the moment when the beam passing through one ofsaid' apertures begins to go out from the cell, the beam passing throughanother aperture just begins. to impinge on said cell. In that way thetotal amount of light received by the cell remains constant. If there isno .screenon the path of the beams, no variation of current occurs andconsequently no sound can be perceived in the loud speaker; on thecontrary if there is a screen the amount of light can be varied at will,said variation being reproduced at a frequency depending on the speed atwhich the apertures of the disc succeed one another in front of thecell.

The screen can be made with'a part quite opaque the other having aconstant translucency, the breadth of the translucent zone in'adirection perpendicular to thedisplacement of the beam being variableand equal to the ordinate of a curve representing the vibratory law ofthe desired tune. Thus if the apertures in the disc are shaped in formof sumciently narrow slots, the quantity of light impinging on the cellat any moment shall be proportional to the ordinate of said curve. I

It will therefore be able to reproduce the tone of an instrument if wehave plotted the corresponding curve.

- Figure 1 shows by way of example such a modulating screen; a curve ofsinusoidal shape representing a period of a simple sonorous vibration(0A being the axis of the ordinates and OC the axis of the time) istraced on a rectangular transparent plate OABC and the upper surface ofthe plate limited by the sinusoid is blackened.

If a thin rectilinear beam of light EH1, is directed on this frame OABCperpendicularly to the axis of the time 00, the quantity of lightpassing through the screen will be proportional-to the ordinate HH ofthe curve. If, therefore, the screen is swept by such beams of light,for instance, from the left to the right and in such a manner that abeam of light passes out through BC at the moment when another beam oflight enters through 0A the curve representing, as a function of thetime, the quantity of light passing through the screen, will becontinued and reproduce exactly the shape or form of the curve traced onthe screen. In the example of Figure 3, this curve is a sinusoid thefrequency of the oscillations being equal to the number of passages perunit of time of the beams of light on the screen. If therefore thescreen is swept for instance 435 times per second and if the light whichhas passed through the screen is sent to a cell, the cell generates afrequency current 435 which is transmitted to a loud speaker andproduces the tone-value indicated by the symbol laa. This symboldesignates the musical note produced at the end of the third octave ofthe keyboard of an ordinary piano and corresponds to a note produced atthe rate of 435 vibrations per second. If instead of tracing a simplesinusoid on the screen OABC, a more complex curve containing harmonicsof the fundamental frequency is traced, sounds with different timbrewill be produced according to the number and amplitude of theseharmonics.

The plotting of said curve is easy if we know the relative intensitiesof the harmonics of the tone, in another way said curve may be obtainedexperimentally, say by means of an oscillograph.

Instead of the black or white screen above described, a screen ofvariable translucency can be used, the law of variation of thetranslucency in the direction of the displacement of the beam being thatrepresented by the former curve.

Of course the variation of the cell current must follow exactly andimmediately those of the amount of light impinging on the cell, inconsequence this latter must be of the type called devoid of inertia,such as the potassium cells and not as the selenium ones.

The screens can be operated by keys and by stops similar to those usedin organs, said keys or stops being connected to the screens byintermediary of means either mechanical or electrical.

The following disclosure and the hereby annexed drawings show as exampleseveral forms of execution of the invention.

Figure 1 represents a modulating screen as described above.

Figures 2 and 3 represent diagrammatically in plan and in elevation asimple embodiment or constructional form of the apparatus constitutingthe subject matter of the invention wherein the sweeping of themodulating screen is obtained by means of a disk having slots androtating in front of a luminous source.

Figure 4 is a front view of the disk with slots.

Figures 5, 6 and '7 relate to the modulating screens.

Figures 8 to 11 represent special screens allowing of varying theintensity of the tone as a function of the time.

Figures 12 to 16 show modulating screens allowing of obtaining thesuccessive harmonics of a fundamental note.

Figure 17 shows the method of obtaining by synthesis a complex tonehaving numerous harmonies.

Figures 18 and i9 relate to an embodiment wherein the keys of the pianoare adapted to receive two distinct displacements adapted to vary theintensity and the timbre of the tone.

An exact luminous source 1 arranged in the focus of a condenser 2furnishes a parallel beam of light. This beam of light falls on a disk 3which is mounted on a shaft 4 and driven at a perfectly constant speedby a motor 5 through the medium of toothed gearing 4.

The disk 3 consists of opaque material and has a certain number ofequidistant narrow slots 6 disposed according to the radii of a certainnumber'of concentric rings '7 (Figure 4) This disk may consist, forinstance, of glass covered with a photographic emulsion on whichtransparent lines representing the slots have been recorded on an opaquebase.

The different rings 7 have numbers of different equidistant slots, therings having the smallest number of slots are disposed in the center ofthe disk and the rings having the largest number of slots are on theperiphery.

If, for instance, twelve dozen rings of slots are arranged on the disk 3and if one chooses for the numbers of slots of the successive ringsnumbers proportional to the frequencies of the successive notes of agamut, it will be obvious that with a suitable speed of rotation of thedisk 3, it is possible that the numbers of slots of the successive ringsdefiling per second in front of a fixed point opposite correspondingrings will be equal to the frequencies of the successive notes of thegiven gamut. By doubling the speed of rotation of the disk, a higheroctave is obtained while by reducing-this speed one half a lower octaveis obtained.

Another opaque disk 8 having the same axis as the previous one but fixed(Fig. 5) is disposed behind the disk 3 and at a small distancetherefrom. The said opaque disk 8 is provided opposite each ring ofslots of the disk 3 with a window 9 formed by a curvilinear rectanglelimited by z two radii of the disk and by two arcs of concentriccircles, the height of this window 9 being equal to the height of theslots 7 and its width, that is to say the space between the two radiiwhich limit same, being equal to the distance between two consecutiveslots '7 of the corresponding ring 6 so that one of the slots appears inthe window at the exact moment when the other leaves same.

The different slots of a ring of the disk 3 are presented successivelyon one of the edges of the window 9 of the disk 8 to disappear on theother edge after having swept continuously the surface of this window.The time which elapses between the moment when the slot appears and themoment when it disappears determines the period of the sonorousvibration which is subsequently produced: the slots of a ring beingequidistant and the speed of the disk 3 being constant, the said periodwill be perfectly constant so that the height of the tone produced byeach ring will be well determined. In order to produce a tone, oneapplies the method of modulating (which is indicated at the beginning ofthe application) the quantity of light passing through the window 9. Forthis purpose, there is provided in this window a modulating screen 10according to the screen OABC of Figure 1 on which has been traced aperiod of a sinusoidal curve by taking as axis of the time one of thearcs of the circle limiting the window 9 and bearing the ordinatesaccording to the radii. Since the modulating screen 10 is opaque on oneside ofthe curve and transparent on the other side, the quantity oflight transmitted through each window 9 (quantity which is constantowing to the absence of the screen 10) now varies in a periodical mannerrelative to the sweeping frequency.

As explained above, the harmonics are furnished by the form of the curveof the modulating screen 10 and thus determine the timbre of the tone;different timbres are obtainable by changing the form of said curve.This variety of timbre is obtained by providing according to thedifferent radii of the disk 8 other series of Windows etc. bearingmodulating screens of different form or shape. A simple rotation of thedisk 8 then allows of the changing of the desired timbre.

In practice, the disk 8 is made of glass covers with a photographicemulsion and is merely provided on an opaque base with transparentsurfaces limited by the modulating curves.

After having cleared the disk 8, the luminous rays are immediatelycollected again by means of a collecting lens 11. This lens has for itsobject to produce a real image of the luminous source 1. As this sourceis very exact, the rays are collected again.

An objective 12 placed in line has for its object to produce on themirrors 13 integral with the keys 14 real (enlarged) images of thewindows 9 of the disk 8. The focal distance of the objective 12 and itslocation are selected in such a manner that the real images of thewindows 9 are produced through the optical system (formed by the lenses11 and 12) on the line adjoining the centers of the mirrors 13 andhaving a spacing equal to that of the consecutive keys 14 of the piano.Owing to this selection, each key 14 is in optical relation with thecorresponding disk ring which determines the pitch of the sound, that isto say the corresponding note, (the timbre being determined by the formor shape of the modulating screen 10). A small mirror 13 is connected toeach key 14 of the piano. This mirror is adjusted in such a manner thatnormally this mirror does not fall in the beam of light: in other words,it is outside the opening of the real image of the window produced bythe lenses l1 and 12.

When the key 14 is depressed, the mirror 13 is tilted and brought in thebeam of light at 13'. It

is thus possible to return the luminous rays to an optical system 15which has for its object to collect the rays and concentrate them on aphotoelectric cell 16. v

The orientation of the different mirrors 14 and the arrangement of theoptical system 15 are selected in such a manner that all the luminousrays are receivedv on the cell 16.

By depressing different keys, the performer therefore adjusts a certainnumber of mirrors 13 in such a manner that the corresponding luminousmodulation is concentrated on the cell. Since each note receives amodulation of light, whose intensity is well determined, it is thuspossible to form musical chords.

The selection of the form or shape of the curve of the modulating screenallows of modifying at will the timbre by displacing a register to suitthe performer whereby a modulating screen is ient to limit the number ofrings to the twelve notes corresponding to an octave In order to extendthe apparatus to several octaves, one may either employ severalphotoelectric cells connected in parallel to the ampliher or concentrateon a single cell the luminous rays from several different opticalsystems, each corresponding to an octave. In Figures 2 and 3 there isshown on one side of the system just described a second identical systemcomprising a source 11, a disk 31, rotating twice as fast as the disk 3,etc., and corresponding'to the octave higher 7 than the preceding one.flected by the mirrors ofoetave are returned to cell 16 as before.

Fig. 6 shows a. screen which may be disposed in front of the window 9 onthe path of the luminous beam and by means of which one may obtainsounds having different tones. Said screen is constituted by an opaqueregion on a ground of uniform translucency. If, for instance, said curveis a whole period of a sinusoid, there will be obtained the fundamentalnote correspohding to the frequency with which the beams succeed oneanother upon the screen. If for instance, said separating curve hasforits equation the former note and its octave will be obtained. Thus,generally, any tone can be reproduced at will, by choosing forseparating curve one period of the curve representing the vibration lawcorresponding to said tone.

Fig. 7 shows another arrangement allowing to obtain the same result.This one consists in a screen whose translucency is modulated (in thedirection of the movement of the beam) byscales of shades suitablydetermined succeeding to one another; it is obvious it can bemade insuch a manner, that the amount of light passing through the screen whileit is swept by the beam is modulated exactly as in the former case.

It is also possible to reduce the number of the concentrical series ofslots of the disc to twelve each of which corresponds to one note of thegamut; one of those series is in reality able to give not only thefundamental note but also its The luminous rays rethe keys of thissecondthe same photoelectric octaves by inserting suitable screens,corresponding to the first, second, fourth, eighth, etc., harmonics ofthe fundamental notes being similar to those indicated by the numeral 1,can be actuated by the keys corresponding to the different octaves. Itis obvious that in such case a single disc can be suflicient.

To obtain, for instance, a sound which decreases with time, there may beinterposed on the path of the light beam passing through the screen anauxiliary screen as the one represented on Fig. 9, narrowingprogressively the breadth (direction perpendicular to the displacement)of the beam impinging on the modulating screen. Such screen can be alsoa disc entirely dark with suitable slots disposed on a circumference.

Such a screen for instance this of Fig. 9, for imitating the pianofortetone, is caused, by lowering a key, to rotate at uniform speed, makingone turn during the whole holding of the note. The light beams impingeon said screen which, when the note begins, presents the breadth EF,allowing the passage of the 'wholebeani, said breadth narrowingprogressively while the disc is rotating in the arrow direction,presenting successively for the passage of beam breadths EF'--E"F and soon.

The tone of-some instruments say the hunting horn corresponds topulsations of intensity having a very low frequency, say 8 or 10 persecond. Fig. 8 represents an aut'ziiiary screen with slots whos; lengthvaries. periodically, causing thus, when rotating at uniform speed, theintensity of light impinging on the cell to vary according to the samelaw. Instead of these slots there may be drawn upon the screen acirc'dar strip whose translucency should vary periodic: v.

It is often not enough to modify with time the intensity; the tone mustalso be altered; such is th:. 1C for the violin with which the tonevaries a coming to the position of the fiddlestick. Fig. 10 shows adevice allowing to obtain said result. Scales of shades corresponding tothe successive tones of the instrument are registered side by side onthe successive radii of a circle; one interposes on the beam path atevery moment the corresponding scale.

Some instruments, such as the pianoforte, owe their musical value to thepresence of several strings having a slight difference of frequency.

This result may be imitated by disposing on a rotating screen concentricseries of equal number of slots the distribution of which varies fromone series to the next.

Fig. 11 shows such an arrangement with two series of unequally spacedslots.

At last the synthesis of a sound by its harmonics can be obtained bymeans of several screens with scales of shades correponding to thesuccessive harmonics, and whose displacement in the convenient directionallows to modify the phase and the amplitude of each harmonic.

Fig. 12 shows a scale of shades corresponding to the fundamental note;if on said screen is drafted a straight line perpendicular to thedirection of the movement of the beam (horizontal on the figure) allalong this line the opacity of the screen varies according to a linearlaw, if a line is drawn parallel to the displacement of the beam, allalong this second line the opacity varies according to a sinusoidal lawwhose period corresponds to this of the fundamental note.

Figures 13, 14, 15, 16 represent in the same way the scales of shadescorresponding to the first, second, third and fourth harmonics, theopacity varying in the same manner according to a linear and asinusoidal law, the period of this latter, being the half the third, thefourth and the fifth of that of the fundamental.

In order to obtain a determined tone we superpose the screens of Figs.12, 13, 14 and so on, each having with reference to the screen 12corresponding to the fundamental note, a peculiar shifting in thedirection of the movement of the beam, which determines the phase of thecorresponding harmonic, and another shifting in a' perpendiculardirection which determines the relative intensity of this same harmonic.

Fig. 1'7 shows said scales of shades shifted in both directions in frontof the window through which the beam sweeps the cell with the desiredfrequency.

Fig. 18 is a plan view of a pianoforte keyboard allowing, by only asuitable displacement of the key, to determine the tone and theintensity of the sound.

Fig. 19 is a cross view of the same.

The keys are arranged so that they can be given a displacement from topto bottom in order to adjust the intensity and another displacement fromfront to rear in order to modify thetune, both movements beingdetermined by the p y rs finger.

For that purpose the key 57 is for instance maintained on a verticalresilient slip 59, which is fastened to a slide 60 slidable in a block61. A spring 62 returns the key to its first or normal position.

The movement from top to bottom actuates the bell crank 63 which movesthe screen 64 whose opacity varies according to a linear law in thedirecti-i perpendicular to that of the sweeping. The displacement fromfront to rear by intermediary of the connecting rod 65 actuates thescreen 66 upon which are drafted side by side, in the directionperpendicular to the sweeping direction, shades corresponding each tothe tone of one special instrument.

Things are arranged in such a manner that the light beam 6'7, modulatedat the desired fundamental frequency, crosses one after the other thetwo screens 64 and 66.

With such device, it is possible with only one instrument to reproducethe tones of many quite different musical instruments.

What is claimed is:

1. A muscal instrument comprising a plurality of keys and stops, asource of light, a photoelectric cell without inertia, an acousticreceiver actuated by the variations of current in said cell, meansactuated by the keys to cause beams of light comng from the source toimpinge on the cell, in the path of said light beams, windows, rotatingdiscs with concentrical series of slots. the distance from one slot tothe next one and the dimensions of the windows being such that one beambegins to impinge on the cell just at the moment when the next oneleaves it, means to rotate the discs at uniform speed, means forinterposing in the path of the light beam, screens modulating accordingto any predetermined law the amount of light passing through them, whilethey are swept by.the light beam.

2. A musical instrument comprising a large number of keys and stops, aluminous source, a photoelectric cell without inertia, an acousticreceiver actuated by the variations of current of the said cell,rotating disks having concentric series of slots and placed behind theluminous j source, opaque screens placed behind the said rotatingdisks,window'sin the said screens disposed opposite concentric series ofslots of the rotating disks, the dimensions of the windows and thedistance of two consecutive slots being such that a beam of light comingfrom the source and passing through one of these slots enters a windowat the moment when the preceding beam issues therefrom, mirrors integralwith the keys disposed so as to receive when actuated the beams of lightpassing through the windows and reflected on the photoelectric cell,means for disposing in the path of the beams of light screens oftranslucency periodically variable in the direction of the displacementof the beams of light so as to be able to modulate according to apredetermined law the quantity of light which is transmitted to thecell.

3. A musical instrument comprising a plurality of keys and stops, 9.source of light, a

photoelectric cell without inertia, an acoustic receiver actuated by thevariations of current in said cell, means actuated by the keys to causebeams of light coming from the source to impinge on the cell, in thepath of said light beams, rotating discs with concentrical series ofslots,

I windows, the dimensions of the windows and the distance from one slotto the next one being such that one beam begins to impinge on the celljust at the moment where the next one leaves it, means to rotate ihediscs at uniform speed, mean: operated by the stops for interposing onthe path of the light beams, screens some of which have differenttranslucency on their points, said translucency varying according to asinusoidal law in the direction of the displacement of the beam;

and according to a linear one in the direction perpendicularto saiddisplacement, the means actuated by the stops allowing to interposeseveral of said screens on the path of the light beams, with shiftingfrom one to another in the direction or the displacement of the beamsand In a direction perpendicular to the same.

4. A musical instrument comprising a plurality of keys and stops, 2.source of light, a photoelectric cell without inertia, an acousticreceiver actuated by the variations of current in said cell, meansactuated by the keys to cause beams of light coming from the source toimpinge on the cell, in the path of said light beams, windows, rotatingdiscs with concentrical series of slots, the dimensions of the windowsand the distance from one slotto the next one being such that one beambegins to impinge in the cell just at the moment where the next oneleaves it, means to rotate the discs at uniform speed, rotatable discsdisposed on the path of the light beam and having parts to allow passageto light arranged on' a circumierence concentric to the shaft of therotatable discs and having variable lengths so as to allow, by

rotating the screen, to vary the amount of light impinging on the cellin order to produce damping effects, and means responsive to theoperation,

of the stops for rotating said discs.

5. A musical instrument comprising a plurality of keys, a source oflight, a photoelectric cell without inertia, an acoustic receiveractuated by its variations of current, means to cause beams of lightcoming from the source to impinge on the cell; in the path of said lightbeams, windows, rotating discs with concentrical series of slots, thedimensions of the windows and the distance from one slot to the next onebeing such that one beam begins to impinge on the cell just at themoment where the next one leaves it, means to rotate the discs atuniform speed, means actuated by depressing the keys to interpose in thepath of the light beams, a screen with variable translucency to vary,according to the depressionof the key, the amount of light falling onthe cell, means actuated by giving to the key a displacement from frontto rear to insert in the path of the light beams a screen modulating theamount of light passing through it while it is swept by the light beams,the modulation law varying in reference with the more or lessdisplacement of the key.

6. In a musical instrument according to claim 5, a single rotating discwith twelve concentrical series of slots, each series corresponding to anote of the gamut, means responsive to the displacement from front torear of a key for inserting in the path of the beam passing through theseries of slots corresponding to the same note as the key, a screen, thescreens being so designed that the screen actuated by a note of thesecond, third, and so on octave gives, by modulating the beam of light,the first, third, etc. harmonic of the corresponding note in the lowestoctave.

PIERRE MARIE GABRIEL TOULON.

